The present invention relates to a tire tube manufacturing method for molding a tube material by an extrusion process and subsequently for vulcanizing the tube material by a vulcanizing process, and to a tire tube manufactured by the manufacturing method.
When the radial load acts on a vehicle wheel mounted with a tube-incorporated tire, the tire and the tube are subjected to deformation with the load. However, particularly when the tire runs on a hard obstacle such as a rock during off-road traveling, or when the vehicle jumps and touches the ground, the tube is pressed hard between the tire largely deformed and a metal rim, there occurs in some cases the rim-hitting phenomenon that the inner wall surfaces of the tube abut against each other. If the inner wall surfaces of the tube abut against each other because of such rim-hitting phenomenon, the durability of the abutment portion may decrease in some cases.
The decrease in the durability of the abutment portion stated above can be prevented, as proposed by Japanese Patent Application Laid-open No. 9-164806, by providing a projection of a thick portion on the wall surface of the tube for reinforcement, which wall surface is likely to be decreased in durability by the rim-hitting phenomenon.
It should be noted here that when a tube material is extrusion-molded by the extrusion process in the tire tube manufacturing process, the optimum extrusion speed for extruding each part of the tube material varies with the thickness of the tube material. Therefore, if a projection of a thick portion is provided on the wall surface of the tube for reinforcement, the optimum extrusion speed for the extrusion of the thick portion will differ from the optimum extrusion speed for the other portion, presenting the problem that the extrusion molding of the whole part of the tube material cannot be efficiently accomplished.
The present invention has been accomplished with the above circumstances in view, and it is an object of the present invention to provide a tire tube manufacturing method which enables manufacture of a tube material having a thick portion for reinforcement to be efficiently carried out.
To accomplish the above-described object, according to a first aspect and feature of the present invention, there is provided a tire tube manufacturing method for molding a tube material by an extrusion process and subsequently for vulcanizing the tube material by a vulcanizing process, in which the thickness of a tube body portion and the thickness of a rib-shaped projection are set substantially equal to each other when the tube material integrally having the tube body portion of an annular cross section and the rib-shaped projection extending in the longitudinal direction of and protruding from the tube body portion is extruded by the extrusion process.
With the above arrangement, not only the provision of the rib-shaped projection can prevent a decrease in tube durability caused by the rim-hitting phenomenon but also the approximate equalization of the thickness of the tube body portion and the thickness of the rib-shaped projection enables extrusion molding of the tube material to be efficiently accomplished.
Furthermore, according to a second aspect and feature of the present invention, in addition to the above-described arrangement, there is provided a tire tube manufacturing method in which the tube material has a plurality of rib-shaped projections which are disposed adjacent to each other.
With the above arrangement, the plurality of rib-shaped projections can effectively protect a wide range of the tube.
According to a third aspect and feature of the present invention, there is provided a tire tube manufacturing method for molding a tube material by an extrusion process and subsequently for vulcanizing the tube material by a vulcanizing process, in which the thickness of a tube body portion and the thickness of two rib-shaped projections are set substantially equal to each other when the tube material integrally having the tube body portion and the rib-shaped projections is extruded by the extrusion process, the tube body portion having an annular cross section, and the rib-shaped projections extending in the longitudinal direction of the tube body portion and protruding from an inner peripheral surface of the tube body portion, and in which base end portions of the rib-shaped projections are disposed at a higher level than tip end portions thereof when the tube material is vulcanized and molded by the vulcanizing process.
With the above arrangement, not only the provision of the rib-shaped projection can prevent a decrease in tube durability caused by the rim-hitting phenomenon but also the approximate equalization of the thickness of the tube body portion and the thickness of the rib-shaped projections enables the extrusion molding of the tube material to be efficiently accomplished. Besides, since the base end of the two rib-shaped projections is arranged at a higher level than the tip end portion thereof at the time of vulcanization molding of the tube material, it is possible to effectively protect a wide range of the tube by permitting the rib-shaped projections to be suspended by gravitation until they are situated along the inner peripheral surface of the tube body portion.
According to a fourth aspect and feature of the present invention, there is provided a tire tube integrally having a tube body portion of an annular cross section and the rib-shaped projection extending in the longitudinal direction of and projecting from the tube body portion, the thickness of the rib-shaped projection being substantially equal to that of the tube body portion.
With the above arrangement, the provision of the rib-shaped projection not only can prevent a decrease in tube durability caused by the rim-hitting phenomenon but also enables extrusion molding of the tube body portion of the tube material and rib-shaped projection to be carried out simultaneously and efficiently.
According to a fifth aspect and feature of the present invention, in addition to the fourth aspect and feature described above, there is provided a tire tube having a plurality of rib-shaped projections which are disposed adjacent to each other.
With the above arrangement, the same effect as that of the second aspect and feature can be obtained.
According to a sixth aspect and feature of the present invention, there is provided a tire tube integrally having a tube body portion of an annular cross section and two rib-shaped projections extending in the longitudinal direction of the tube body portion and protruding from an inner peripheral surface of the tube body portion, wherein the thickness of the tube body portion and the thickness of the rib-shaped projections are set substantially equal to each other, and the rib-shaped projections are arranged along the same circumferential direction as the tube body portion.
With the above arrangement, the same effect as that of the third aspect and feature can be obtained.